> The rough gist of the argument is that only legislatures are empowered to choose the method of selection of electors, and therefore governors (like Texas's governor) or courts (as in North Carolina) that order changes to election procedure render the entire count of the election invalid.

It’s a bad argument. The US Congress has delegated some of its power to the Executive Branch (FDA and IRS, among others), just like I’m sure some of these states have. If a state legislature passed laws allowing the governor to change election rules, then the legislature is still choosing the electors, not directly, but by having delegated that power to the executive branch of the state.

I’m not a lawyer but this argument sounds flimsy at best.